Abstract

The timescale and integration of human whole body and cellular Hsp72 adaptations during the initial phase of human-heat acclimation were determined. Two exercise humid-heat exposures on consecutive days lowered exercise rectal temperature (P < 0.05) and heart rate (P < 0.01). Sweat rate was increased (P < 0.001) during exercise through an improved maintenance of sweating, and sweat Na+ reabsorption was enhanced (P < 0.05). These adaptations were accompanied by a reduced Hsp72 mRNA response with no change in protein level. Two prolonged, low-intensity exercise-heat bouts on consecutive days are sufficient to initiate physiological and Hsp72 mRNA adaptations, although Hsp72 protein adaptation may require a greater exercise intensity or longer acclimation period.